1. Field of the Invention
The present invention relates to a keyboard chassis for a keyboard instrument, which is applied to a keyboard instrument, such as an electronic piano, and configured to support a plurality of keys and hammers in a state arranged in the left-right direction, and more particularly to a construction of a keyboard chassis formed as a molded article made of a synthetic resin and a key guide structure for guiding a key pivotally moved by key depression.
2. Description of the Related Art
Conventionally, the present applicant has already proposed a keyboard chassis for an electronic piano in Japanese Laid-Open Patent Publication (Kokai) No. 2005-70644. A keyboard device of the electronic piano having the keyboard chassis includes a plurality of keys extending in a front-rear direction and a plurality of hammers provided for the keys, respectively, and the keyboard chassis pivotally supports the keys and hammers. The keyboard chassis is formed as a molded article made of a synthetic resin, such as an ABS resin. The keyboard chassis of the whole electronic piano is formed by connecting a plurality of keyboard chassis each corresponding to one octave in the front-rear direction form.
The keyboard chassis made of a synthetic resin is configured such that a rear part thereof (referred to as “the chassis rear” in this section) pivotally supports keys, and further, a front part thereof (referred to as “the chassis front” in this section) guides each key pivotally moved by key depression and supports a hammer associated with the key and moved in a manner interlocked with the key depression. Further, the keyboard chassis is provided with a multiplicity of vertical ribs that connect between the chassis rear and the chassis front while maintaining a space therebetween for pivotal motion of each hammer. Specifically, each vertical rib is formed in a plate shape having a predetermined thickness in a left-right direction and is disposed in a manner dividing between hammers adjacent to each other in the left-right direction.
Further, conventionally, the present applicant has already proposed a key guide structure for a keyboard instrument in Japanese Laid-Open Patent Publication (Kokai) No. 2000-122654. A keyboard device of an electronic piano to which the key guide structure is applied includes a plurality of keys each extending in a front-rear direction and having an inverted U shape in cross-section formed by a top wall and left and right walls, and a keyboard chassis holding these keys in a state arranged in a left-right direction and pivotally supporting each key by a rear end thereof. A key guide is provided on the keyboard chassis for each key for guiding the key being pivotally moved. Further, in this keyboard device, each key and keyboard chassis are both formed as molded articles made of a hard synthetic resin. Each key guide is erected below a front end or its vicinity of a key associated therewith and is formed in a plate shape having a lateral width substantially equal to a distance between left and side walls of the key, with a lubricant such as grease applied to left and right sides of the key guide.
Further, there has also conventionally been proposed another key guide structure for a keyboard device in Japanese Laid-Open Patent Publication (Kokai) No. H11-296162. A key guide described in this publication is formed by mounting a guide member made of rubber on a guide member-holding part formed in a manner projecting upward. The guide member is formed in a hollow cylindrical shape and is mounted on the guide member-holding part in a state having the guide member-holding part inserted into the inside thereof.
In the key guide structures as proposed in Japanese Laid-Open Patent Publication (Kokai) No. 2000-122654 and Japanese Laid-Open Patent Publication (Kokai) No. H11-296162, when a key is in a key-released state, an upper end of the associated key guide is engaged with the key in a state slightly inserted therein. In this key-released state, when the key is depressed, the key guide is engaged with the key in a manner deeply inserted therein, thereby guiding the key being pivotally moved such that the key is prevented from swinging in the left-right direction, i.e. while preventing lateral swing of the key.
In the keyboard chassis described above, relatively high rigidity thereof is ensured by provision of a multiplicity of vertical ribs that connect the chassis rear and the chassis front. However, since the number of vertical ribs is large, the amount of a synthetic resin used as a material for molding the keyboard chassis is increased. Of course, it is possible to reduce the amount of used material for the keyboard chassis by reducing the number of vertical ribs.
However, in such a case, there arises the following problem: Assuming that the electronic piano is stored in a room in an upright position in which the left and right sides thereof are in vertically opposite positions, if the room temperature becomes very high e.g. in summer, the vertical ribs made of a synthetic resin tend to be bent downward due to the self weight of the keyboard chassis and the weight of the hammers, which can cause deformation of the keyboard chassis. In this case, there is a possibility that when a key is depressed, a hammer associated therewith cannot be smoothly moved or that noise is generated due to rubbing of the pivotally moved key or hammer against the keyboard chassis.
On the other hand, as to the key guide structure, in Japanese Laid-Open Patent Publication (Kokai) No. 2000-122654 mentioned above, the keys and key board chassis are made of a hard synthetic resin, and hence when the lubricant applied to the key guides becomes short due to long-term use of the electronic piano, noise can be generated by rubbing of the inner surfaces of each key against the key guide when sliding thereon. Further, in a case where the amount of lubricant applied to the key guide is too much, there can arise a problem that the lubricant can leak out of the key. On the other hand, in Japanese Laid-Open Patent Publication (Kokai) No. H11-296162, sine the guide member is formed in a hollow cylindrical shape which covers the outside of the guide member-holding part, the amount of a material used for forming the guide member becomes relatively large, resulting in increased costs.